Which of the following best describes the relationship between depth and partial pressure of gases?

The correct answer is that depth increases partial pressure. As a diver descends into the water, the weight of the water above them increases, which also increases the pressure exerted on their body and the gases they are breathing. The relationship is governed by Boyle’s Law, which states that as the volume of a gas decreases, the pressure increases, assuming temperature remains constant.

In the context of diving, as the pressure increases with depth, the partial pressure of each gas in a mixture (like air) also increases. For instance, at sea level, the partial pressure of oxygen is approximately 0.21 bar (21% of atmospheric pressure). However, at a depth of 10 meters (about 33 feet), the total pressure is approximately 2 bar due to the extra pressure from the water column, causing the partial pressure of oxygen to rise to around 0.42 bar. This is crucial for divers to understand because it affects how gases are absorbed and eliminated from the body, which has implications for safe diving practices and managing the risks of decompression sickness.

Understanding this relationship is vital for safe diving operations, particularly regarding the planning of dives and managing ascent rates to avoid complications such as nitrogen narcosis and decompression illness.